1. Field of the Invention
The present invention relates to an information processing apparatus and method, and particularly, to an information processing apparatus and method capable of reducing the memory capacity demanded when a reversibly-encoded code stream is transformed to an irreversibly-encoded code stream.
2. Description of the Related Art
In the related art, digital image data are used in a variety of fields such as film production, medical services, or still image capturing. Generally, such digital image data are processed by setting uncompressed image data as master images, compressing the uncompressed image data as necessary, and delivering the compressed file via a network or writing the compressed file to a recording medium.
For example, in the field of the digital cinema, the DCI (Digital Cinema Initiatives) standard specifies a compression format for delivering a film. In this format, the ISO (International Organization for Standardization) standard, JPEG2000 (Joint Photographic Experts Group 2000), Part-1 which is an irreversible compression encoding scheme is employed as a compression/decompression technology, of which the bit rate is 250 Mbps as a peak rate for a moving picture sequence of 4096×2160 pixels at XYZ12 bits (24 Hz). That is, uncompressed master images are compressed and then delivered or screened.
Since the master image having a large data size is inconvenient to store, the master image is usually stored by reducing the data amount without data loss using a reversible compression.
For example, the image resolution specified in the DCI standard is 4096×2160 pixels, four times of the HDTV (High Definition Television). Therefore, since the data amount of the uncompressed image data is larger, in practice, the master image is usually stored as a reversible compression file which is encoded using a reversible compression.
In this case, such a reversible compression file is transformed to a JPEG2000 file of the DCI standard in which the file is compressed using an irreversible compression scheme. However, in the JPEG2000 standard, a wavelet transform filter is different between a reversible compression encoding scheme and an irreversible compression encoding scheme. Therefore, during this transform, it may be necessary to restore the baseband image once.
A typical transcoder for executing this process decodes all of the code streams of the reversible compression file to restore the baseband image having the same data size as that of the original baseband master image.
Meanwhile, a downdecoder was proposed which executes an inverse discrete cosine transform using only the coefficient for a low-frequency component in a DCT block of bit streams of a high resolution image to decode the high resolution image into a standard resolution image (e.g., refer to Japanese Patent Nos. 4016166 and 4026238).